public class Node{
    public int value;
    public Node left;
    public Node right;
    public Node(int data){
        this.value=data;
    }
}

public void recursionTree(Node head){
    if(head==null)return;

    System.out.print(head.value+" ");
    recursionTree(head.left);
    recursionTree(head.right);
    //前：中左右
}

public void recursionTree(Node head){
    if(head==null)return;

    recursionTree(head.left);
    System.out.print(head.value+" ");
    recursionTree(head.right);
}

public void recursionTree(Node head){
    if(head==null)return;

    recursionTree(head.left);
    recursionTree(head.right);
    System.out.print(head.value+" ");
}